Communication system using relayed radio channels

ABSTRACT

In a communication system, a communication control apparatus is disposed in a mobile object. The communication control apparatus relays information exchanged between a plurality of radio terminals carried into the mobile object and a network side. The communication control apparatus comprises a communication control server which performs establishment of a radio channel between it and a base station at the network side, and establishment of a radio channel between it and a radio terminal according to a communication request from the radio terminal, and a communication unit which performs a radio communication with the radio terminal and a radio communication with the base station, using each radio channel established by the communication control server. The communication control server has an agent function for providing a communication reservation or a packet transmission to a user of a radio terminal in case that it cannot establish a radio channel between it and the base station corresponding to a communication request at a point of time when it has received the communication request from the radio terminal.

TECHNICAL FIELD

The present invention relates to a communication system, a communicationcontrol method and a communication control apparatus for performingcommunication by wireless between a radio terminal and a network.

BACKGROUND ART

In recent years, mobile radio communication services spread and a word“mobile computing” also has taken root in general. A mobile computationbeing in wide use at the present time is performed by connecting apersonal computer through an adapter to a portable telephone subscribingto a mobile radio communication service. FIG. 11 shows an embodiment ofa communication system in which a mobile computation of this kind isperformed.

In FIG. 11, 1-1 designates a mobile station for performing a mobilecomputation, and is composed of a personal computer 1 a, a radioterminal 1 b, and an adapter 1 c for connecting both of them with eachother. The radio terminal 1 b designates a radio terminal subscribing toa mobile radio communication network service, and is a portabletelephone for example.

2-1 to 2-h designate base stations of a mobile radio communicationnetwork, and each of them performs communication through a radio channelwith the radio terminal 1 b. 3 designates a mobile radio communicationswitching control means having a function as a mobile radiocommunication switching station and a function as a mobile radiocommunication control station. 4 designates a public network. The mobileradio communication switching control means 3 is connected with thispublic network. 5 designates a LAN of a corporation for example and isconnected with the public network 4.

In the configuration described above, when a user originates a call fromthe personal computer 1 a through the radio terminal 1 b to a desiredservice access point, a radio channel is established between the radioterminal 1 b and one of the base stations 2-1 to 2-h under control ofthe mobile radio communication switching control means 3, and a channelfor linking the base station and the desired service access point witheach other is established. Using a communication channel thusestablished, the user can receive an information providing service froma provider through the public network 4 by means of the personalcomputer 1 a, and can access a LAN 5 of a corporation. In this case, theradio terminal 1 b provides a function as a modem for performing a radiocommunication with the base station to the personal computer 1 a.

Furthermore, a system is utilized in which a mobile station can beconnected with a LAN or an Internet provider by accessing an interfaceto a network operator, and can receive an information service from a LANand the like by means of packet transfer through a radio channel and thesystem is based on the same principle as the configuration shown in FIG.11. A system of this kind is disclosed by, for example, pp.6 to 9 of“NTT DoCoMo Technical Journal”, July 1997 issued by NTT MobileCommunication Network, Inc.

Thanks to such technologies as described above, a mobile radiocommunication service which has mainly provided voice communicationservices up to now is evolving to a service supporting not only datacommunication, particularly such data communication by telephoneconnection as a personal computer communication but also a LANconnection.

It is thought that technologies utilizing a mobile radio communicationnetwork will develop to a radio LAN taken in a broad sense in whichradio terminals can be connected with each other through a radio channeland can freely move over a wide area.

In the future, however, in case of attempting to provide variouscommunication services (data communications, voice communications andthe like) utilizing such a mobile radio communication network asdescribed above, the following problems will happen.

(1) Since a communication channel between a mobile station and a desiredservice access point includes a radio channel, in case that the radiochannel is not good or the mobile station is not within the radioservice zone of a base station, the mobile station cannot receive acommunication service. In such a case, if a mobile station is within thesphere of daily action, a user can find out a communicable area and takea measure such as performing communication within the area or the like.However, when a user is moving by car or train, such a measure cannot betaken.

(2) Particularly, when a user inside a high-speed mobile object such asa train on the Shinkansen Line or the like attempts to perform a datacommunication, a circuit interruption is frequently caused duringcommunication by influence of tunnels or opencuts. Therefore, it is notpossible to provide efficient and user-friendly services.

(3) Furthermore, when a circuit interruption occurs frequently asdescribed above and the number of incompleted calls is increased, anoverhead operation for connecting a call becomes useless as a result,and the efficiency of a communication system is lowered.

(4) In order to build such a radio LAN taken in a wide sense asdescribed above, it is necessary to always make an original LANenvironment capable of being used as it is at a place to which aterminal (a radio terminal or a mobile station in this case) has movedeven in case that each of terminals moves over a wide area. However,since a former technology utilizing a mobile radio communication networkis insufficient in agent functions, it is difficult to make each radioterminal always utilize an original LAN environment at a place to whichthe radio terminal has moved.

DISCLOSURE OF INVENTION

The present invention is based on the consideration of suchcircumstances as described above, and an object of the present inventionis to provide a communication system, a communication control method anda communication control apparatus which can provide a user-friendlycommunication service to a radio terminal user even under a poorcommunication environment.

In order to attain such an object, a communication system according tothe present invention disposes a communication control apparatus betweena radio terminal and a network side. In a preferable embodiment, eachradio terminal is carried into a mobile object and a communicationcontrol apparatus is arranged in advance in such a mobile object.

A communication control apparatus relays the exchange of informationbetween a radio terminal and a network by performing a radiocommunication with the radio terminal and by performing a radiocommunication with a base station.

The communication control apparatus is provided with a communicationcontrol server for performing a radio channel control between it and aradio terminal and for performing a radio channel control between it anda base station, and a communication unit for performing a radiocommunication with a radio terminal and a radio communication with abase station using radio channels established by the communicationcontrol server.

Main control functions included in channel control functions provided bythe communication control server are as follows:

In case that a communication control server has received a communicationrequest from a radio terminal and the server cannot rapidly establish aradio channel between it and the base station in response to thecommunication request, the server transmits a notification indicating toreject the communication request to the radio terminal.

In another embodiment, in case that a communication control server hasreceived a communication request from a radio terminal and the servercannot rapidly establish a radio channel between it and the base stationin response to the communication request, the server reserves thecommunication request. The server starts communication between the radioterminal and the network side when the server has established the radiochannel. That is to say, in case that the server cannot provide a realtime communication requested by a user, it provides an alternative meansas the second best measure.

In a further other embodiment, in case that a communication controlserver has received a communication request from a radio terminal andthe server cannot rapidly establish a radio channel between it and thebase station in response to the communication request, the server sendsa packet transmission request to the radio terminal. When a packet hasbeen transmitted from the radio terminal, the server stores the packet.The server transmits the packets thus stored to the network when it hasestablished the radio channel between it the base station.

Additionally to these, a communication server provides to a radioterminal such various agent functions as a control function and the likein case that it has received communication requests of plural kindsbeing different in priority from one another from radio terminals.

According to the present invention, since a communication controlapparatus performs a channel control between it and a network sideinstead of a radio terminal, load on the radio terminal side islightened. Furthermore, it is possible to provide a user-friendlycommunication service in which a communication state between a radioterminal and a network side is hidden to a user of each radio terminalby means of agent functions provided in the communication controlapparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the overall configuration of a communication systemaccording to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the composition of a communicationcontrol apparatus of the same embodiment.

FIG. 3 is a flowchart showing operation of a communication controlapparatus of the same embodiment at the time of requestingcommunication.

FIG. 4 is a flowchart showing operation in mode 2 of a communicationcontrol apparatus of the same embodiment.

FIG. 5 is a flowchart showing operation in mode 3 of a communicationcontrol apparatus of the same embodiment.

FIGS. 6 to 8 are flowcharts showing operation of variation examples ofthe same embodiment.

FIG. 9 is a block diagram showing the composition of a communicationcontrol apparatus of a second embodiment of the invention.

FIG. 10 is a block diagram showing the composition of a communicationcontrol apparatus of a third embodiment of the invention.

FIG. 11 shows the whole configuration of a former communication system.

BEST MODE FOR CARRYING OUT THE INVENTION A: First Preferred Embodiment(1) Configuration of This Embodiment

FIG. 1 is a block diagram showing the configuration of a communicationsystem according to a first preferred embodiment of the presentinvention.

A communication system according to this embodiment is composed ofcomponents at a mobile object side and components at a network side.

First, components of a mobile object side are described.

In FIG. 1, each of “10-j” (j=1 to n) is a mobile object. These mobileobjects are, for example, such a passenger coach capable ofaccommodating plural radio terminals as a train on the Shinkansen Lineor other railway vehicles, a bus and a passenger boat. These mobileobjects may be such a vehicle other than a passenger vehicle as anambulance.

A communication control apparatus 10 and one or more radio terminals11-j (j=1 to m) under the communication control apparatus 10 arearranged in each mobile object 10-j.

Each radio terminal 11-j (j=1 to m) can perform an informationtransmission between it and a network side through the communicationcontrol apparatus 10. The kind of information to be transmitted and theform of transmission between it and the network side are not limited inparticular. That is to say, each radio terminal can exchange variouskinds of information such as voices, data and the like between it andthe network side. Each radio terminal can perform an informationtransmission between it and the network side in various forms of achannel switching type traffic, a packet switching type traffic and thelike.

Each one of the radio terminals 11-j (j=1 to m) is carried by apassenger or the like into a mobile object 10-j, and is a publicly knownradio terminal using an existing technology. Each radio terminal is forexample a portable telephone using a PDC method, a device made up of apersonal computer, a portable telephone connected and an adapterconnecting them each other, or a PDA having a radio device built in it,but may be some device other than these. This embodiment can beimplemented without applying any improvement to these radio terminals.

This embodiment is mainly characterized by the communication controlapparatus 10 to provide a user-friendly communication service (describedlater) to each user of a radio terminal even in a poor communicationenvironment.

This communication control apparatus 10 is composed of a communicationcontrol server 10 a, a communication unit 10 b, and a plurality ofantennas 10c-j (j=1 to k) for communicating with radio terminals.

The communication control server 10 a has the following functions.

a. Mode 1

In the mode 1, the communication control server 10 a establishes at oncea radio channel between the communication unit 10 b and the network sidein response to a request from a radio terminal 11-j, and provides acommunication service using this radio channel to the radio terminal11-j. That is to say, in this mode 1, the communication control server10 a provides a real time communication service to a user. In this mode1 and in modes 2 and 3 described later, a channel between a radioterminal 11-j and the communication control apparatus 10, and a channelbetween the communication control apparatus 10 and the network aredifferent from each other. A radio terminal 11-j does not perform adirect access to the network side.

b. Mode 2

In the mode 2, in case that the communication control server 10 a cannotmeet a communication request from a radio terminal 11-j for a reasonthat a channel state between it and the network is not good and thelike, it performs reservation for the communication request. Whencommunication has become possible, the communication control server 10 asends the reserved communication request to the network side andestablishes a radio channel, and provides a communication service usingthis radio channel to the radio terminal 11-j.

c. Mode 3

The mode 3 is a mode in which the communication control server 10 aexhibits its agent functions. In the mode 3, when the communicationcontrol server 10 a cannot meet a communication request from a radioterminal 11-j for a reason that a channel state is not good and the likebut the radio terminal side needs the communication, the communicationcontrol server 10 a accepts a packet transmission request. That is tosay, the communication control server 10 a reserves data packets from aradio terminal 11-j in storing means such as a buffer or the like notillustrated, and transmits the data packets thus reserved to the networkside, utilizing a period during which a channel state between it and thenetwork side is good.

One of the modes 1 to 3 described above is selected, for example,according to setting of a switch provided on the communication controlapparatus 10.

In addition to such mode setting by a switch as described above, it cando also to set a mode according to the information for specifying themode, the information being sent by wireless from the network side.Every mobile object does not have to be provided with a communicationcontrol apparatus provided with the modes 1 to 3, but some mobile objectmay be provided with a communication control apparatus provided withonly one or two operation modes out of the modes 1 to 3.

Next, as shown in FIG. 2, the communication unit 10 b is composed of aradio terminal side interface unit 20, a network side interface unit 21,and an antenna 22.

The radio terminal side interface unit 20 performs communication with aradio terminal 11-j (j=1 to m) through one of the antennas 10c-j (j=1 tok). The network side interface unit 21 performs communication with thenetwork side through an antenna 22.

Next, components of the network side are described.

In FIG. 1, 12-j (j=1 to m) designate base stations of a mobile radiocommunication network. These base stations perform communication withthe communication control apparatus of the mobile objects 10-j (j=1 ton) or a mobile station other than these.

13 designates mobile radio communication switching control means whichhas a function as a mobile radio communication switching station and afunction as a mobile radio communication control station.

The function as a mobile radio communication switching station includessuch controls as registration of position of a mobile object or a mobilestation, tracking telephone exchange, authentication at the time of datatransmission, accounting and the like.

The function as a mobile radio communication control station includes achannel control and the like between a base station and a mobile objectand the like.

The mobile radio communication switching control means 13 is connectedwith a public network 14. The public network 14 has LANS 15-j (j=1 to n)connected with it.

In this embodiment, each radio terminal in each mobile object 10-j (j=1to n) is connected with one of the LANs 15-j (j=1 to n) of the networkside if necessary, and is united with the LAN into one body to form amobile LAN. As means for forming such a mobile LAN, the LANs 15-j (j=1to n) are respectively provided with mobile IP (Internet Protocol)agents 16-j (j=1 to n) and the mobile radio communication switchingcontrol means 13 is provided with a mobile IP agent 17.

Describing in more detail, this is as follows:

Ordinarily, a terminal connected with a LAN recognizes its LANenvironment and then receives a service provided through the LAN.Components of a communication environment of a LAN in this case are, forexample, a method for giving an IP address, a name server advice,setting of a fireball, a proxy server address and the like.

In order to make a terminal connected with a LAN be able to freely move,it is necessary to make the terminal be able to use its originalcommunication environment as it is also in a place to which it hasmoved.

A technology for solving such a problem is a mobile IP technology.

In a system shown FIG. 1, the mobile radio communication switchingcontrol means 13 and the LANs 15-j (j=1 to n) each are provided with amobile IP agent.

There is an IPinIP as a typical mobile IP of these mobile IPs. When acommunication channel, for example, between the communication controlapparatus 10 of a mobile object 10-j and a LAN 15-j is established by amobile IP of this kind, a radio terminal 11-j in this mobile object 10-jcan be connected through the communication control apparatus 10 to a LAN15-n of the network side, and thanks to this, communication between theradio terminal 11-j and the LAN 15-n can become possible.

(2) Operation of This Embodiment

FIGS. 3 to 5 are flowcharts showing operation of a communication controlapparatus in this embodiment. Operation of this embodiment is describedwith reference to these figures in the following, taking as an example acase where a radio terminal 11-j in a mobile object 10-j originates acall in order to perform connection with a LAN 15-1.

First, as shown in FIG. 3, a communication request is outputted from theradio terminal 11-j (step S1). This communication request contains theaddress of a service access point which is an entrance of the LAN 15-1.

When the communication control server 10 a receives this communicationrequest (step S2), it outputs a status inquiry to the communication unit10 b (step S3).

When the communication unit 10 b receives this status inquiry (step S4),it detects a communication status, namely, whether or not a good radiocommunication can be performed with the network side, and sends aresponse containing a result of it to the communication control server10 a (step S5).

When the communication control server 10 a receives the response fromthe communication unit 10 b (step S6), it judges whether or notcommunication can be performed (step S7).

In case that the communication control server 10 a has judged thatcommunication can be performed, it performs a process for establishing achannel (step S8). That is to say, it generates communication requestinformation for requesting connection with the service access point.Next, the communication control server 10 a establishes a channelreaching the service access point by sending this communication requestinformation through the communication unit 10 b to a base station of thenetwork side (step S10), and sends a communication request response tothe radio terminal 11-j (step S9). The communication unit 10 b which hasreceived the communication request response starts data communicationwith the LAN 15-1 (step S11).

On the other hand, in case that the communication control server 10 ahas judged that communication cannot be performed in step S7, itperforms a process corresponding to a mode set at the present time (stepS13).

First, in case that mode 1 is set, the communication control server 10 arejects a communication request from the radio terminal 11-j (step S14),and issues a rejection of communication request to the radio terminal11-j (step S15). As a result, the radio terminal side ends processingthe communication request.

Next, it is assumed that mode 2 has been set when it judges thatcommunication cannot be performed in step S7. Operation in this caseresults in following a flow shown in FIG. 4.

First, the communication control server 10 a performs reservation of thecommunication request (step S16). That is to say, in order to preparefor an opportunity of transmission being expected to come after that, itstores the communication request information containing the address ofthe service access point.

Next, the communication control server 10 a outputs a status inquiry tothe communication unit 10 b (step S17).

When the communication unit 10 b receives this status inquiry (stepS18), it detects a communication status and sends a response containingthe detected communication status to the communication control server 10a (step S19).

When the communication control server 10 a receives this response (stepS20), it judges whether or not communication can be performed (stepS21).

In case that the communication control server 10 a has judged thatcommunication can be performed, in the same way as steps S8 to S10 inFIG. 3 described above it performs a communication request process forestablishing a channel (step S22), transmission of a communicationrequest response to the radio terminal 11-j (step 23), and transmissionof a communication request to the communication unit 10 b (step S24).

The communication unit 10 b which has received the communication requestresponse starts a data communication with the LAN 15-1 (step S25).

On the other hand, in case that the communication control server 10 ahas judged that communication cannot be performed in step S21, itperforms again reservation of the communication request to thecommunication unit 10 b.

Following this, until it is judged that communication can be performed aprocess from step S17 to S21 is repeated.

Actually, a timer (not illustrated) starts clocking in response to acommunication request from the radio terminal 11-j. In case that it isnot judged that the communication request can be accepted by the timewhen this timer ends clocking, the communication control server 10 arejects the communication request and issues a communication requestincompletion notification to the radio terminal 11-j at the timer endtiming.

Next, it is assumed that mode 3 has been set when it is judged thatcommunication cannot be performed. Operation in this case results infollowing a flow shown in FIG. 5.

First, the communication control server 10 a sends a packet transmissionrequest to the radio terminal 11-j (step S26).

When the radio terminal 11-j receives this packet transmission request(step S27), it transmits a packet to the communication control server 10a (step S28).

When the communication control server 10 a receives this packet, itstores this packet into such storing means not illustrated as a bufferand the like (step S29).

Then the communication control server 10 a performs reservation of apacket transmission channel for the radio terminal (step S30). That isto say, the communication control server 10 a starts performing aprocess of establishing a radio channel for transmitting a packet fromthe radio terminal 11-j.

First, the communication control server 10 a outputs a status inquiry tothe communication unit 10 b (step S31).

When the communication unit 10 b receives this status inquiry (stepS32), it sends a response containing a communication status to thecommunication control server 10 a (step S33).

When the communication control server 10 a receives the response fromthis communication unit 10 b (step S34), it judges whether or notcommunication can be performed (step S35).

In case that the communication control server 10 a has judged thatcommunication can be performed, the communication server 10 aestablishes a radio channel between it and the network side for theradio terminal 11-j having the packet transmission channel reserved andtransmits a packet from the radio terminal 11-j which packet is storedin the storing means to the network side (steps S36 and S37).

Then, the communication control server 10 a issues a packet transmissioncompletion notification to the radio terminal 11-j (step S38), and theradio terminal 11-j recognizes the packet transmission completion (step39).

On the other hand, in case that the communication control server 10 ahas judged that communication cannot be performed, it performs againreservation of a packet transmission channel for the communication unit10 b (step S30). After this, a process of steps S30 to S35 is repeateduntil it is judged that communication can be performed in step S35.

According to this embodiment described above, the following effects canbe obtained.

a. Since a communication control apparatus disposed in a mobile objectperforms a channel control between it and a network side instead of eachradio terminal in the mobile object, load on the radio terminal side islightened. For example, in case that a radio terminal is used inside amobile object in this embodiment, it is possible to reduce thetransmission output of the radio terminal to about {fraction (1/100)} ofthat of a former radio terminal and suppress consumption of a battery.

b. Thanks to an agent function of a communication control apparatus, itis possible to provide a user-friendly communication service where acommunication status between a user terminal and a network side ishidden to each user of a radio terminal.

c. Since a useless call to a network side which becomes an incompletedcall is suppressed, an overhead operation of the network side can bereduced. Furthermore, the completed-call probability is improved and aradio channel is effectively utilized.

(3) Variation Examples

Variation examples of the first embodiment are described in thefollowing.

First Variation Example

This variation example is obtained by replacing the flow of FIG. 3 inthe first embodiment with a flow shown in FIG. 6. The steps shown alsoin FIG. 3 out of steps shown in FIG. 6 are given the same step numbersas those given in FIG. 3. Since the steps prior to step S13 in FIG. 6are the same as those shown in FIG. 3, illustration of them is omitted.

In this variation example, a user can send plural kinds of communicationrequests from a radio terminal to a communication server. The user cangive a priority order to each of these communication requests. In thisvariation example, these communication requests are handled in order ofpriority.

For example, suppose a case in which a real time communication requestis sent as the first preference and a packet transmission request issent as the second preference from a radio terminal to a communicationcontrol server in a state where mode 1 is set.

In this case, if the real time communication request of the firstpreference has been rejected due to shortage of channels and the like,the process proceeds through step S7 (see FIG. 3) and step S13 to stepS101. The communication control server judges whether or not the packettransmission of the second preference can be performed. Hereupon, incase that the packet transmission can be performed, the communicationcontrol server sends a packet transmission permission notificationcontaining conditions for the packet transmission to the radio terminal(step S102). In case that a packet transmission cannot be performed, arejection of request comes to be performed in the same way as the firstembodiment (step S14).

When the radio terminal receives the packet transmission permissionnotification, it judges whether or not a packet transmission isnecessary (step S103), and if necessary, it notifies the communicationcontrol server that it performs the packet transmission (step S104).

As a result, according to the flow shown in FIG. 5, a packettransmission is performed from the radio terminal to the network sidethrough the communication control server and the communication unit.Since the flow of a packet transmission was already described in thefirst embodiment with reference to FIG. 5, the duplicated description isomitted here.

According to this variation example as described above, even in casethat the communication control server cannot meet a real timecommunication request of the first preference from a radio terminal, itcan meet a packet transmission request of the second preference ifpossible, and can provide a user-friendly service.

Second Variation Example

This variation example is obtained by replacing the flows of FIGS. 4 and5 in the first embodiment with flows shown in FIGS. 7 and 8. The stepsshown also in FIGS. 4 and 5 out of steps shown in FIGS. 7 and 8 aregiven the same step numbers as those given in FIGS. 4 and 5.

This variation example improves the operation in case that a real timecommunication request from a radio terminal cannot be satisfied and acommunication reservation (mode 2) is performed.

First, suppose a case in which a real time communication request is sentfrom a radio terminal to a communication control server when mode 2 isset, and this real time communication request is rejected due toshortage of channels and the like. In this case, the process proceedsthrough step S7 (see FIG. 3) to step S16 of FIG. 7 and the communicationcontrol server performs a reservation process for the communicationrequest (steps S16 to S21).

When the communication control server comes into a state where it canaccept a packet transmission during the reservation process for thiscommunication request, the communication control server sends a packettransmission permission notification containing conditions for thepacket transmission to the radio terminal (step S110).

When the radio terminal receives this packet transmission permissionnotification, it judges whether or not the packet transmission isnecessary (step S111). If the packet transmission is not necessary, theradio terminal sends a transmission-unnecessary notification to thecommunication control server (step S112). When the communication controlserver receives this transmission-unnecessary notification, it returnsto a reservation process for a real time communication (steps S16 toS21).

On the other hand, in case that a packet transmission is necessary instep S111, the radio terminal sends a packet transmission notificationto the communication control server (step S113).

As a result, according to a flow shown in FIG. 8, a packet transmissionis performed from the radio terminal to, the network side through thecommunication control server and the communication unit. Since contentsof a packet transmission are the same as those already described in thefirst embodiment with reference to FIG. 5, the duplicated description isomitted here.

When the packet transmission has been completed, the communicationcontrol server sends a transmission completion notification to the radioterminal (step S38) and judges whether or not communication is reserved(step S114). In case that communication is reserved, the communicationcontrol server returns to step S16 (FIG. 7).

When a real time communication has come to be capable of being performedduring a packet transmission process, the communication control serverperforms preferentially a real time communication process having a highpriority order. In this case the packet transmission process being inthe course of processing is stopped.

According to this variation example, even in case that a communicationcontrol server cannot meet a real time communication request from aradio terminal and is performing a communication reservation process, itcan meet a packet transmission request from the radio terminal ifpossible, and so it is possible to provide a user-friendly service.

Third Variation Example

In this variation example, a data converting means is disposed between aradio terminal side interface unit 20 and a network side interface unit21. As the data converting means, for example, a transmission speedconverting means such as a buffer and the like is conceivable. In caseof using the transmission speed converting means, for example, it ispossible to perform control so as to perform a packet communicationbetween a base station and a communication control server and perform acontinuous communication having a low speed of 9600 bps, 32 kbps or thelike between the communication control server and a radio terminal.

Fourth Variation Example

In mode 3 (packet transmission mode) of the embodiment, a communicationcontrol server stores a packet from a radio terminal in a buffer, andthis buffer is limited in capacity. Therefore, if a packet being toolarge in size is transmitted from a radio terminal, the packet cannot befully stored in the buffer (namely, the packet is lost) and the radioterminal results in retransmission of the packet and so the transmissiondelay of a packet is increased. Conversely, if a packet being too smallin size is transmitted from a radio terminal, a time until a certainamount of data is stored in the buffer is lengthened and a delay timeuntil each packet is transmitted to a network side is made long.Thereupon, in this variation example, a communication control serverpresents the maximum size of a packet capable of being stored in abuffer to each radio terminal, and controls each radio terminal totransmit a packet being proper in size. Thanks to this, it is possibleto minimize the delay time in packet transmission and prevent occurrenceof a packet loss.

Fifth Variation Example

In the embodiments described above, a judgement is made as to judgewhether or not a radio communication can be performed between a networkside and a radio terminal by means of a communication unit. In thisvariation example, a further detailed judgement is performed. That is tosay, even in case that a mobile object is within the service area of abase station, a situation in which for example a voice communication canbe performed but a broad-band communication cannot but be rejected mayoccur depending upon the amount of traffic passing the base station atthat point of time. Thereupon, in this variation example, acommunication unit takes radio resources capable of being provided to auser in a mobile object, and a communication control server provides acommunication service within this taken resources. For example, in casethat available radio resources are deficient, a communication controlserver controls the communication speed. For example, in case that abroad-band communication request has been received when available radioresources are deficient, the communication control server performscontrol so as to perform reservation for the communication request andperform a processing corresponding to the reserved communication requestat a point of time when sufficient radio resources have been secured.

Sixth Variation Example

This variation example adds a mobile Internet protocol to thecommunication control server 10 a in FIG. 1. In this case, it ispossible to form a LAN containing radio terminals 11-j (j=1 to m) assubnets obtained by partitioning them with routers and accommodate sucha LAN as a subordinate of the communication control apparatus 10. Inthat case, each radio terminal 11-j accommodated in a subnet canremotely use a LAN environment in a LAN 15-j (j=1 to n) accessed by thecommunication control server 10 a even if the radio terminal 11-j doesnot have a mobile Internet protocol in itself.

Seventh Variation Example

This variation example provides a communication control apparatus 10 ina fixed space such as a home office instead of a mobile object and makesit perform a channel control between a radio terminal near it and a basestation.

B: Second Preferred Embodiment

FIG. 9 is a block diagram showing the composition of a communicationcontrol apparatus 10 in a second preferred embodiment of the presentinvention. The second embodiment of the invention is described withreference to FIG. 9 in the following. Components in FIG. 9 correspondingto the components of the first embodiment are given the same symbols asthe first embodiment and description of them is omitted.

Generally, in a mobile radio communication, for example when a railwayvehicle comes into a tunnel or when an automobile runs on a road beingpoor in visibility, a transmission loss is increased and communicationis liable to become impossible.

On the other hand, however, in case of such a mobile object as a railwayvehicle, a regular bus or a regular truck whose running schedule isfixed in place and time, it is possible to estimate a time when it willcome into a radio jamming area such as a tunnel from its runningschedule. In addition, it is possible to correct a time when it willcome into a communication jamming area on the basis of compensation datasuch as its running position, running speed, running time and the likeby checking its actual running state, and predict accurately a happeningtime of communication jamming.

And also in such a mobile object as an automobile having no fixedrunning schedule, it is possible to estimate occurrence of acommunication jamming by detecting a communication obstacle existing inthe forward direction of the mobile object by means of a radar and thelike.

Thereupon, in this embodiment, as shown in FIG. 9, a mobile radiocommunication control apparatus 10 is provided with a detecting means30. This detecting means 30 is means which estimates a time when acommunication jamming will happen on the basis of a moving state of amobile object and other data and informs a communication control server10 a in advance that the time will come. As a manner for informing of atime when a communication jamming will happen in this case, thefollowing manners are conceivable, for example.

a. To compute the hours when a communication jamming is expected tohappen at regular time intervals and report one by one the predictedhours of occurrence of communication jamming to the communicationcontrol server 10 a.

b. To compute the hours when a communication jamming is expected tohappen at regular time intervals and notify in advance the communicationcontrol server of occurrence of a communication jamming at a point oftime when a communication jamming is estimated to happen after aspecified time (after 30 seconds for example).

In this embodiment, the following operation is performed by utilizingsuch a detecting means 30.

First, when a communication request is given from a radio terminal 11-j,the communication control server 10 a judges whether or not acommunication jamming will happen in a specified time on the basis of areport from the detecting means 30.

In case that the communication control server 10 a has judged acommunication jamming will happen in a specified time, it sets thecommunication request from the radio terminal as a channel reservationstate.

After this, in case that a predicted time of occurrence of acommunication jamming has elapsed and it is judged that a goodcommunication can be performed at that point of time, the communicationcontrol server 10 a establishes a communication channel between theradio terminal 11-j and the network side according to the reservedcommunication request.

Furthermore, for example, when the radio terminal 11-j is performingcommunication, it may be judged that a communication jamming will happenin a specified time. In this case, the communication control server 10 aterminates once the communication of the radio terminal 11-j andreserves the communication.

After this, in case that a predicted time of occurrence of acommunication jamming has elapsed and it is judged that a goodcommunication can be performed at that point of time, the communicationcontrol server 10 a re-establishes a reserved channel and restartscommunication between the radio terminal 11-j and the network side.

According to this embodiment, since occurrence of a communicationjamming due to coming into a communication jamming area is estimated anda channel connection with a network side is performed utilizing a periodin which no communication jamming happens, it is possible to prevent achannel interruption during communication and provide a user-friendlycommunication service.

C: Third Preferred Embodiment

FIG. 10 is a block diagram showing the composition of a communicationcontrol apparatus 10 in a third preferred embodiment of the presentinvention.

In this embodiment, the communication control apparatus 10 is providedwith a judging means 40 for judging validity of a radio terminal 11-j.

The judging means 40 judges the validity of a radio terminal 11-j withrespect to a communication request from the radio terminal 11-j, andoutputs the result of judgement to the communication control server 10a. The communication control server 10 a performs a channel establishingprocess for the radio terminal 11-j only in case that it has been judgedthat the radio terminal 11-j has a system validity.

The judging means 40 may inquire of a switching station at the networkside or another radio terminal about the system validity of the radioterminal 11-j without judging by itself the system validity of the radioterminal 11-j.

Concretely, this embodiment is effective to such a system as a publictelephone system in which communication is performed by mounting aprepaid card, a credit card or the like into a radio terminal 11-j.

In case of applying this embodiment to such a system, the judging means40 judges the validity of a radio terminal 11-j by inquiring of anaccounting apparatus of a credit card company about such a useridentification as a credit card number and a password, or checking forthe remainder left in a prepaid card with an accounting apparatus of aswitching station at the network side.

According to this embodiment, it is possible to prevent an illegal useof a radio terminal.

What is claimed is:
 1. A communication system comprising: acommunication network; one or plural base stations connected with thecommunication network; one or plural radio terminals; and acommunication control apparatus disposed between the radio terminal andthe base station for relaying information exchanged between the radioterminal and the network by performing a radio communication with theradio terminal and performing a radio communication with the basestation; wherein said communication control apparatus comprises: acommunication control server for performing a channel control betweensaid communication control server and a respective radio terminal, andfor performing a channel control between said communication controlserver and a base station; a communication unit for performing a radiocommunication with the radio terminal and the base station using radiochannels established by the communication control server; and whereinsaid communication unit detects a communication status with thecommunication network and said communication control server determineswhether or not radio communication can be performed with thecommunication network.
 2. A communication system according to claim 1,wherein the communication control apparatus is disposed in a mobileobject and performs the relaying operation intended for a radio terminalinside the mobile object.
 3. A communication system according to claim1, wherein the communication control server comprises means fortransmitting a rejection of communication request to a radio terminal inresponse to a communication request received from the same radioterminal, in case that the communication control server cannot establisha radio channel corresponding to the communication request whenreceiving the communication request.
 4. A communication system accordingto claim 3, wherein the communication control server comprises means forreserving a communication request received from a radio terminal and forstarting communication between the radio terminal and the network sideafter establishing a radio channel for the communication, in case thatthe communication control server cannot establish a radio channelcorresponding to the communication request when receiving thecommunication request.
 5. A communication system according to claim 3,wherein the communication control server comprises means for sending apacket transmission request to a radio terminal in response to acommunication request received from the same radio terminal, and forstoring packets which are received from the radio terminal, and fortransmitting the packets thus received to the network after establishinga radio channel for transmitting the packets between the communicationcontrol server and a base station, in case that the communicationcontrol server cannot establish a radio channel corresponding to thecommunication request when receiving the communication request.
 6. Acommunication system according to claim 3, wherein the communicationcontrol server comprises means for receiving a plurality ofcommunication requests having different priority from a radio terminal,and performing control of a radio channel between the communicationcontrol server and a base station corresponding to a communicationrequest which is one of the communication requests and has a prioritylower than a priority of other communication request when thecommunication control server cannot respond to the communication requesthaving higher priority.
 7. A communication system according to claim 3,wherein the communication control server comprises: (a) means forbringing a real time communication request received from a radioterminal into a reserved state when the communication control servercannot rapidly establish a radio channel between the communicationcontrol server and a base station in response to the real timecommunication request; (b) means for sending a packet transmissionpermission notification to the radio terminal when a packet transmissioncan be accepted during the communication reservation; (c) means forstoring packets which are transmitted from the radio terminal andtransmitting the packets to the network side by seizing an opportunityat which the transmission is possible; and (d) means for making theradio terminal start communication corresponding to the communicationrequest being in a reserved state when the communication control serverhas established a radio channel for the communication between thecommunication control server and a base station.
 8. A communicationsystem according to claim 3, wherein the communication control servercomprises means for converting to each other data sent and receivedbetween the communication control server and a radio terminal, and datasent and received between the communication control server and a basestation.
 9. A communication system according to claim 3, wherein thecommunication control server comprises a mobile Internet protocol forcontrolling communication with a LAN.
 10. A communication systemaccording to claim 6, wherein the communication control server comprisesmeans for presenting the size of a packet capable of being stored to theradio terminal.
 11. A communication system according to claim 3, whereinthe communication unit comprises means for detecting radio resourcescapable of being provided to the radio terminal, and the communicationcontrol server performs control for providing a communication service tothe radio terminal within the detected radio resources.
 12. Acommunication system according to claim 1, wherein the communicationcontrol apparatus comprises detecting means for estimating a time when acommunication jamming will happen and, on the basis of the result ofestimation, controlling how to handle a communication request from theradio terminal.
 13. A communication system according to claim 1, whereinthe communication control apparatus comprises judging means for judginga system validity of a radio terminal which has performed acommunication request.
 14. A communication system according to claim 2,wherein the mobile object is a railway vehicle, an automobile, or aship.
 15. A communication control method for controlling radiocommunication performed between at least one radio terminal and acommunication network comprising the steps of: providing a communicationcontrol apparatus disposed between the radio terminal and a base stationof the communication network; detecting a communication status betweenthe radio terminal and the communication network with the communicationcontrol apparatus; determining whether or not radio communication can beperformed with the communication network and the radio terminal with thecommunication control apparatus; and establishing radio channels betweenthe radio terminal and the communication network to relay informationbetween the radio terminal and the communication network by performing aradio communication with the radio terminal and performing a radiocommunication with the base station using the communication controlapparatus based on the determination made above.
 16. A communicationcontrol method according to claim 15, wherein the communication controlapparatus transmits a rejection of communication request to a radioterminal in response to a communication request received from the sameradio terminal, in case that the communication control server cannotestablish a radio channel corresponding to the communication requestwhen receiving the communication request.
 17. A communication controlmethod as defined in claim 15, wherein the communication controlapparatus reserves a communication request received from a radioterminal and starts communication between the radio terminal and thenetwork side after establishing a radio channel for the communication,in case that the communication control apparatus cannot establish aradio channel corresponding to the communication request when receivingthe communication request.
 18. A communication control method as definedin claim 15, wherein the communication control apparatus sends a packettransmission request to a radio terminal in response to a communicationrequest received from the same radio terminal, and stores packets whichare received from the radio terminal, and transmits the packets thusreceived to the network after establishing a radio channel fortransmitting the packets between the communication control server and abase station, in case that the communication control apparatus cannotestablish a radio channel corresponding to the communication requestwhen receiving the communication request.
 19. A communication controlmethod as defined in claim 15, wherein the communication controlapparatus sends a packet transmission request to a radio terminal inresponse to a communication request received from the same radioterminal, and stores packets which are received from the radio terminal,and transmits the packets thus received to the network afterestablishing a radio channel for transmitting the packets between thecommunication control server and a base station, in case that thecommunication control server cannot establish a radio channelcorresponding to the communication request when receiving thecommunication request.
 20. A communication control method as defined inclaim 15, wherein the communication control apparatus presents the sizeof a packet capable of being stored to the radio terminal.
 21. Acommunication control method according to claim 15, wherein thecommunication control apparatus detects radio resources capable of beingprovided to the radio terminal and provides a communication service tothe radio terminal within the detected radio resources.
 22. Acommunication control method according to claim 15, wherein thecommunication control apparatus estimates a time when a communicationjamming will happen and, on the basis of this result of estimation,controls how to handle a communication request from the radio terminal.23. A communication control apparatus comprising: a communicationcontrol server for establishing a radio channel between thecommunication control server and a radio terminal and a radio channelbetween the communication control server and a base station of acommunication network; a communication unit for performing a radiocommunication with the radio terminal and a radio communication with thebase station, using each radio channel established by the communicationcontrol server; and wherein said communication unit detects acommunication status with the communication network and saidcommunication control server judges whether or not the radiocommunication can be performed with the communication network so thatthe communication control server can relay communication between theradio terminal and the communication network.
 24. A communicationcontrol apparatus according to claim 23, wherein the communicationcontrol server comprises means for transmitting a rejection ofcommunication request to a radio terminal in response to a communicationrequest received from the same radio terminal, in case that thecommunication control server cannot establish a radio channelcorresponding to the communication request when receiving thecommunication request.
 25. A communication control apparatus as definedin claim 23, wherein the communication control server comprises meansfor reserving a communication request received from a radio terminal andfor starting communication between the radio terminal and the networkside after establishing a radio channel for the communication, in casethat the communication control server cannot establish a radio channelcorresponding to the communication request when receiving thecommunication request.
 26. A communication control apparatus accordingto claim 23, wherein the communication control server comprises meansfor sending a packet transmission request to a radio terminal inresponse to a communication request received from the same radioterminal, and for storing packets which are received from the radioterminal, and for transmitting the packets thus received to the networkafter establishing a radio channel for transmitting the packets betweenthe communication control server and a base station, in case that thecommunication control server cannot establish a radio channelcorresponding to the communication request when receiving thecommunication request.
 27. A communication control apparatus accordingto claim 23, wherein the communication control server comprises meansfor receiving a plurality of communication requests having differentpriority from a radio terminal, and performing control of a radiochannel between the communication control server and a base stationcorresponding to a communication request which is one of thecommunication requests and has a priority lower than a priority of othercommunication request when the communication control server cannotrespond to the communication request having higher priority.
 28. Acommunication control apparatus according to claim 23, wherein thecommunication control server comprises: (a) means for bringing a realtime communication request received from a radio terminal into areserved state when the communication control server cannot rapidlyestablish a radio channel between the communication control server and abase station in response to the real time communication request; (b)means for sending a packet transmission permission notification to theradio terminal when a packet transmission can be accepted during thecommunication reservation; (c) means for storing packets which aretransmitted from the radio terminal and transmitting the packets to thenetwork side by seizing an opportunity at which the transmission ispossible; and (d) means for making the radio terminal startcommunication corresponding to the communication request being in areserved state when the communication control server has established aradio channel for the communication between the communication controlserver and a base station.
 29. A communication control apparatusaccording to claim 23, wherein the communication control servercomprises means for converting to each other data sent and receivedbetween the communication control server and a radio terminal, and datasent and received between the communication control server and a basestation.
 30. A communication control apparatus according to claim 23,further comprising a mobile Internet protocol for controllingcommunication with a LAN.
 31. A communication control apparatusaccording to claim 23, wherein the communication control servercomprises means for presenting a size of a packet capable of beingstored to the radio terminal.
 32. A communication control apparatusaccording to claim 23, wherein the communication unit comprises meansfor detecting radio resources capable of being provided to the radioterminal, and the communication control server performs control forproviding a communication service to the radio terminal within thedetected radio resources.
 33. A communication system according to claim23, further comprising detecting means for detecting a moving state ofthe communication control apparatus and estimating a time when acommunication jamming will happen, wherein the communication systemcontrols how to handle a communication request from the radio terminalon the basis of this result of estimation.
 34. A communication controlapparatus according to claim 23, further providing judging means forjudging a system validity of a radio terminal which has performed acommunication request.